Turbine airfoil tip shelf and squealer pocket cooling

ABSTRACT

An airfoil comprises leading and trailing edges with pressure and suction surfaces defining a chord length therebetween. The pressure and suction surfaces extend from a root section of the airfoil to a tip section. A tip shelf is formed along the tip section between the pressure surface and a tip shelf wall spaced between the pressure surface and the suction surface. A squealer pocket is formed along the tip section between the tip shelf wall and a squealer tip wall extending from the suction surface. The tip shelf extends from within 10% of the cord length measured from the leading edge to within 10% of the chord length measured from the trailing edge. The squealer pocket extends from within 10% of the chord length measured from the leading edge to terminate between 10% and 25% of the chord length measured from the trailing edge.

STATEMENT OF GOVERNMENT INTEREST

This invention was made with U.S. Government support under Contract No.N00019-02-C-3003 awarded by Department of the Air Force. The FederalGovernment has certain rights in this invention.

BACKGROUND

This invention relates generally to turbomachinery, and specifically toturbine rotor components. In particular, the invention concerns rotorblades for a gas turbine engine.

Gas turbine engines are rotary-type combustion turbine engines builtaround a power core made up of a compressor, combustor and turbine,arranged in flow series with an upstream inlet and downstream exhaust.The compressor compresses air from the inlet, which is mixed with fuelin the combustor and ignited to generate hot combustion gas. The turbineextracts energy from the expanding combustion gas, and drives thecompressor via a common shaft. Energy is delivered in the form ofrotational energy in the shaft, reactive thrust from the exhaust, orboth.

Gas turbine engines provide efficient, reliable power for a wide rangeof applications, including aviation and industrial power generation.Smaller-scale engines such as auxiliary power units typically utilize aone-spool design, with co-rotating compressor and turbine sections.Larger-scale jet engines and industrial gas turbines (IGTs) aregenerally arranged into a number of coaxially nested spools, whichoperate at different pressures and temperatures, and rotate at differentspeeds.

The individual compressor and turbine sections in each spool aresubdivided into a number of stages, which are formed of alternating rowsof rotor blade and stator vane airfoils. The airfoils are shaped toturn, accelerate and compress the working fluid flow, or to generatelift for conversion to rotational energy in the turbine.

Aviation applications include turbojet, turbofan, turboprop andturboshaft engines. In turbojet engines, thrust is generated primarilyfrom the exhaust. Modern fixed-wing aircraft generally employ turbofanand turboprop designs, in which the low pressure spool is coupled to apropulsion fan or propeller. Turboshaft engines are typically used onrotary-wing aircraft, including helicopters.

Turbofan engines are commonly divided into high and low bypassconfigurations. High bypass turbofans generate thrust primarily from thefan, which drives airflow through a bypass duct oriented around theengine core. This design is common on commercial aircraft and militarytransports, where noise and fuel efficiency are primary concerns. Lowbypass turbofans generate proportionally more thrust from the exhaustflow, providing greater specific thrust for use on high-performanceaircraft, including supersonic jet fighters. Unducted (open rotor)turbofans and ducted propeller engines are also known, in a variety ofcounter-rotating and aft-mounted configurations.

Turbofan engine performance depends on precise control of the workingfluid flow, including flow across the airfoil tip. Where clearance,abrasion and temperature effects are of concern, moreover, these factorsoften pose competing design demands on compressor and turbine rotorgeometry, particularly in the tip region of the airfoil.

SUMMARY

This invention concerns an airfoil for a gas turbine engine, for examplea rotor airfoil for a compressor or turbine. The airfoil extends axiallyfrom a leading edge to a trailing edge, defining pressure and suctionsurfaces therebetween. The pressure and suction surfaces extend radiallyfrom a root section of the airfoil to a tip section of the airfoil.

The tip section of the airfoil includes a squealer pocket and a tipshelf. The tip shelf extends along the tip section of the airfoilbetween the concave surface and a tip shelf wall, and the tip shelf wallis spaced between the pressure surface and the suction surface. Thesquealer pocket extends along the tip section of the airfoil between thetip shelf wall and a squealer tip wall, where the squealer tip wallextends along the suction surface.

The tip shelf extends from within 10% of the cord length measured fromthe leading edge to within 10% of the chord length measured from thetrailing edge. The squealer pocket extends from within 10% of the chordlength measured from the leading edge to terminate between 10% and 25%of the chord length measured from the trailing edge.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a gas turbine engine.

FIG. 2 is a perspective view of a rotor airfoil for the gas turbineengine, with a tip shelf and squealer pocket.

FIG. 3 is perspective view of the tip section of the airfoil, showingthe tip shelf and squealer pocket.

FIG. 4 is a perspective view of the tip section of the airfoil, showinganother configuration for the tip shelf.

FIG. 5A is a perspective view of the tip section of the airfoil, showingthe squealer pocket with a squealer discharge flow channelconfiguration.

FIG. 5B is a perspective view of the tip section of the airfoil, showingthe squealer pocket with an alternate squealer discharge flow channelconfiguration.

DETAILED DESCRIPTION

FIG. 1 is a cross-sectional view of gas turbine engine 10, in a turbofanconfiguration. In this configuration, gas turbine engine 10 includespropulsion fan 12 mounted inside bypass duct 14. The power core isformed by compressor section 16, combustor 18 and turbine section 20.Rotor blades (or airfoils) 21 in at least one of compressor section 16and turbine section 20 are provided with squealer tip and tip shelffeature, for improved performance and reliability as described below.

In the two-spool, high bypass configuration of FIG. 1, compressorsection 16 includes low pressure compressor (LPC) 22 and high pressurecompressor (HPC) 24. Turbine section 20 includes high pressure turbine(HPT) 26 and low pressure turbine (LPT) 28.

Low pressure compressor 22 is rotationally coupled to low pressureturbine 28 via low pressure (LP) shaft 30, forming the LP spool or lowspool. High pressure compressor 24 is rotationally coupled to highpressure turbine 26 via high pressure (HP) shaft 32, forming the HPspool or high spool.

In operation of gas turbine engine 10, fan 12 accelerates air flow frominlet 34 through bypass duct 14, generating thrust. The core airflow iscompressed in low pressure compressor 22 and high pressure compressor24, then mixed with fuel in combustor 18 and ignited to generatecombustion gas.

The combustion gas expands to drive high and low pressure turbines 26and 28, which are rotationally coupled to high pressure compressor 24and low pressure compressor 22, respectively. Expanded combustion gasesexit through exhaust nozzle 36, which is shaped to generate additionalthrust from the exhaust gas flow.

In advanced turbofan designs, low pressure shaft 30 is coupled to fan 12via geared drive mechanism 37, providing improved fan speed control forincreased efficiency and reduced engine noise. Propulsion fan 12 mayalso function as a first-stage compressor for gas turbine engine 10,with low pressure compressor 22 performing as an intermediate-stagecompressor or booster. Alternatively, the low pressure compressor stagesare absent, and air from fan 12 is provided directly to high pressurecompressor 24, or to an independently rotating intermediate compressorspool.

Gas turbine engine 10 thus encompasses a range of different shaft andspool geometries, including one-spool, two-spool and three-spoolconfigurations, in both co-rotating and counter-rotating designs. Gasturbine engine 10 may also be configured as a low bypass turbofan, anopen-rotor turbofan, a ducted or unducted propeller engine, or anindustrial gas turbine.

FIG. 2 is a perspective view of rotor airfoil 21 for gas turbine engine10 of FIG. 1. Tip shelf 38 and squealer tip cavity 40 are formed in tipsection 42 of airfoil 21, providing improved tip cooling and resistanceto oxidation, erosion and burn-through.

As installed in the fan or compressor section of a gas turbine engine orother turbomachine, airfoil 21 extends axially from leading edge 44 totrailing edge 46, and radially from root section 48, adjacent innerdiameter (ID platform 50, to tip section 42. Root section 48 typicallyhas fillet radius R along leading edge 44, trailing edge 46 or both,forming a smooth aerodynamic and stress relief transition to platform 50with attachment 51.

Pressure surface 52 (front) and suction surface 54 (back) extend axiallyfrom leading edge 44 to trailing edge 46, defining the profile ofairfoil 21 therebetween. Pressure (concave) surface 52 and suction(convex) surface 54 extend radially from root section 48 and platform 50to tip section 42, defining span height H of airfoil 21.

Tip shelf 38 forms an open radial recess along tip section 42 of airfoil21, extending axially from leading edge 44 to trailing edge 46 alongpressure surface 52. Squealer pocket 40 forms a closed radial recess intip section 42 of airfoil 21, extending axially from leading edge 44 totrailing edge 46, between pressure surface 52 and suction surface 54.

When airfoil 21 is exposed to high temperature flow, for example in theturbine and high pressure compressor sections of a low-bypass turbofanfor military applications, tip section 42 experiences oxidation,erosion, burn-through and other high temperature effects. To addressthis problem, tip section 42 of airfoil 21 is formed with a combined tipshelf and squealer pocket structure, with tip shelf 38 extending alongpressure surface 52, adjacent squealer tip cavity 40 between tip shelf38 and suction surface 54.

Squealer tip cavity (or squealer pocket) 40 maintains a region or pocketof cooling fluid (e.g., air) along tip section 42 of airfoil 21, betweenpressure surface 52 and suction surface 54. Tip shelf 38 maintains aregion or pocket of cooling fluid along pressure surface 52, betweenleading edge 44 and trailing edge 46 in tip section 42. The pockets ofcooling fluid provide a more uniform cooling temperature along tipsection 42, for better oxidation resistance, reduced erosion and lessburn-through.

FIG. 3 is perspective view showing tip section 42 of airfoil 21. Tipshelf 38 extends adjacent pressure surface 52 (front) of airfoil 21,from leading edge 44 to trailing edge 46 along tip section 42. Squealertip cavity 40 extends between tip shelf 38 and suction surface 54 (back)of airfoil 21, from leading edge 44 toward trailing edge 46.

As shown in FIG. 3, tip shelf 38 defines an open (or discontinuous)perimeter radial recess in tip section 42 of airfoil 21. That is, thetip shelf recess is open along pressure surface 52, extending axiallyfrom leading edge 44 to trailing edge 46, with tip shelf 38 definedbetween pressure surface 52 and vertical wall 56.

Vertical (tip shelf) wall 56 extends radially or vertically upward fromtip shelf 38, as shown in FIG. 3, adjacent squealer tip cavity 40. Tipshelf wall 56 also extends axially along tip section 42, from leadingedge 44 to trailing edge 46. Tip shelf wall 56 is thus defined betweentip shelf 38 and squealer tip cavity 40, spaced from pressure surface 52by tip shelf 38, and spaced from suction surface 54 by squealer tipcavity 40.

Tip shelf wall 56 defines a discontinuous or open perimeter cavity fortip shelf 38, extending more than 90% of chord length L between leadingedge 44 and trailing edge 46 of airfoil 21 at tip section 42, or morethan 95% of the chord length. In particular, tip shelf 38 extends alongtip section 42 of airfoil 21 for substantially all of chord length L,including leading edge region A, within 5-10% of chord length L fromleading edge 44, midchord region B, between 5-10% and 90-95% of chordlength L, and trailing edge region C, within 5-10% of chord length Lfrom trailing edge 46.

In this configuration, tip shelf 38 extends substantially all of the wayalong pressure surface 52 to trailing edge 46, for example within 2% or5% of chord length L of trailing edge 46, in order to prevent localizedoxidation in this region. Similarly, tip shelf 38 extends substantiallyall of the way along pressure surface 52 to leading edge 44, for examplewithin 2% or 5% of chord length L of leading edge 44, in order toprevent localized oxidation in that region.

Squealer tip cavity 40 defines a continuous perimeter (or closedperimeter) radial recess in tip section 42 of airfoil 21, between tipshelf wall 56 and squealer tip wall 58. Squealer tip wall 58 extendsaxially along suction surface 54 of airfoil 21 at tip section 42, fromleading edge 44 to trailing edge 46.

Squealer tip wall 58 is coextensive with suction surface 54, and spacedfrom tip shelf wall 56 by squealer tip cavity 40 in midchord region B.Tip shelf wall 56 and squealer tip wall 58 meet in leading edge regionA, along leading edge 44, and in trailing edge region C, along trailingedge 46.

First (tip shelf) and second (squealer tip) walls 56 and 58 define acontinuous or closed perimeter cavity for squealer tip cavity 40, wherecavity 40 extends for more than 75% of chord length L, but less than 90%of chord length L. In particular, squealer tip cavity 40 extends alongtip section 42 of airfoil 21 through midchord region B to leading edgeregion A, within 5-10% of chord length L from leading edge 44. Squealertip cavity 40 also extends along through midchord region B to terminatein aft region D, at least 10-25% of chord length L from trailing edge44.

Squealer tip cavity 40 does not extend into trailing edge region C,within 5-10% of chord length L from trailing edge 44. Thus, tip shelf 38is longer than squealer tip cavity 40 along chord L. This configurationdecreases tip leakage over substantially the entire length of airfoil 21along tip section 42, improving rotor stage efficiency by reducing thetip loss penalty.

Airfoil 21 also includes internal cooling channels 60. Internal coolingchannels 60 provide cooling fluid (air) flow to tip shelf 38 via tipshelf cooling holes 62, and to squealer tip cavity 40 via squealer tipcooling holes 64. In some designs, internal cooling channels 60 alsoprovide additional cooling flow, for example to trailing edge coolingholes or cooling slots 66 along trailing edge 46. In additional designs,leading edge 44 is provided with additional structure, such as leadingedge indentation 68 to improve heat transfer and flow properties alongthe stagnation region.

Tip shelf cooling holes 62 maintain a pocket or region of cooling fluidin tip shelf recess 38, extending between tip shelf wall 56 and pressuresurface 52 of airfoil 21, from leading edge 44 to trailing edge 46 alongtip section 42. Squealer tip cooling holes 64 maintain a pocket orregion of cooling fluid in squealer tip recess 40, extending between tipshelf wall 56 and squealer tip wall 58, from leading edge 44 towardtrailing edge 46 along tip section 42. In addition, tip shelf wall 56forms a lip of metal between tip shelf 38 and squealer tip cavity 40,increasing heat loss and reducing leakage across tip section 42 ofairfoil 21.

The combination of tip shelf 38 and squealer tip cavity 40 also reducesthe heat transfer coefficient across tip section 42, which reduces thenet heat flux into airfoil tip region 42, improving the performance andservice life of airfoil 21. In particular, the heat transfer coefficientmay be substantially proportional to the Reynold's Number, which in turnmay be substantially proportional to the mass flow. The structure of tipshelf 38 and squealer tip cavity 40 reduces mass flow, so the heattransfer coefficient goes down in airfoil tip 42. That is, there is lessheat transfer from the hot gas (working fluid) into airfoil tip section42, resulting in decreases thermal effects and improved service life forairfoil 21.

Additionally, transient thermal strains are reduced due to the removalof hot metal volume with the incorporation of squealer pocket 40.Conventional airfoil tip designs that do not incorporate a squealerpocket have significant hot metal volume locally in the tip region.During transient operation of the gas turbine engine, there isinteraction between the airfoil blade tip surface and the blade outerairseal (BOAS). As a result of this rub/friction interaction, heat isgenerated along the tip airfoil surface due to the frictionalinteraction, and blade airfoil tip metal temperatures become hotter.

Interaction of the blade tip and blade outer airseal is desirable inthat it ensures minimum (or lower) tip clearance during engineoperation. Reductions in tip clearance minimize (or reduce) leakage flowover the blade tip region, with lower losses and increased turbineefficiency. The interaction, however, does not come without penalty toairfoil blade tip cooling performance, impacting durability.

Due to the cyclic nature of gas turbine operations, transient thermalresponse rates of the airfoil metal are relevant to mitigatingcompressive (or thermal) strains. Thermal strains result fromdifferences in the relative transient response rates of local metaltemperatures, including the tip region of the airfoil, whichhistorically has significant hot metal mass that transiently responds ata different (or slower) rate than the surrounding pressure and suctionside walls.

As a result of the difference in relative cooling and heating rates,compressive (or thermal) strain is induced in the airfoil tip regionduring transient operation. In other designs, without the improvementsdescribed here, the cyclic nature of gas turbine engine operations,combined with locally high strain, may result in the initiation andpropagation of thermal mechanical fatigue (TMF) cracking.

To alleviate compressive (or thermal) strains it is desirable to moreclosely match the transient response rates of tip section 42 of airfoil21 with the local airfoil walls 52 and 54. Removing (in operation, hot)metal volume with the incorporation of squealer pocket 40 enables thetransient response of airfoil tip region 42 and airfoil walls 52 and 54to be more closely matched, eliminating (or reducing) a propensity toinitiate and propagate TMF cracks (e.g., through-wall TMF cracks) inairfoil tip region 42, improving durability and performance of airfoil21 in tip region 42 and reducing premature oxidation erosion distress,which effects could otherwise increase airfoil tip clearance and tipleakage flow. The net effect of these improvements to airfoil 21 is animprovement in turbine efficiency and overall engine performance, whichpositively impacts fuel burn and engine on-wing time and service lifeperformance.

FIG. 4 is a perspective view showing tip section 42 of airfoil 21. Tipshelf 38 extends adjacent pressure surface 52 (front) of airfoil 21, asdescribed above, from leading edge 44 to trailing edge 46 along tipsection 42. Squealer tip cavity 40 extends between tip shelf 38 andsuction surface 54 (back) of airfoil 21, from leading edge 44 towardtrailing edge 46.

In this configuration, the length of tip shelf (or trench) 38 isextended through region A to wrap tip shelf 38 around leading edgesurface 44, extending tip shelf 38 onto suction surface (or suctionside) 54 of airfoil 21 in tip section 42. In addition, the length of tipshelf 38 is extended along pressure surface 52 so that tip shelf 38extends through region C to extreme trailing edge surface 46,terminating approximately at the downstream intersection of pressuresurface 52 and suction surface 54.

This example, however, is merely representative. In other designs, tipshelf 38 wraps around leading edge 44 and extends onto suction surface54, but tip shelf 38 does not extend to trailing edge 46. Instead, tipshelf 38 terminates at a location upstream of trailing edge 46 alongpressure surface 52, as described above.

Alternatively, tip shelf 38 extends to extreme trailing edge surface 46,terminating approximately at the downstream intersection betweenpressure surface 52 and suction surface 54, but tip shelf 38 does notwrap around leading edge 44. Instead, tip shelf 38 terminates at extremeleading edge surface 44, or approximately the upstream intersection ofpressure surface 52 and suction surface 54, or tip shelf 38 terminatesat a location downstream of leading edge 44 along pressure surface 52,as described above.

FIG. 5A is a perspective view showing tip section 42 of airfoil 21, withsquealer discharge flow channel 70 extending from squealer tip cavity(or squealer pocket) 40 to trailing edge 46. In this configuration, tipshelf 38 terminates at a location upstream from trailing edge 46, spacedfrom squealer discharge flow channel 70.

Squealer discharge flow channel 70 extends from squealer tip cavity 40to the downstream intersection of pressure surface 52 and suctionsurface 54, at extreme trailing edge surface 46. Squealer discharge flowchannel 70 is configured to reduce the magnitude of vortex flow in tipleakage flow f by axially aligning squealer discharge flow channel 70 attrailing edge 46 and reducing penetration of leakage flow over blade tip42 by discharging a portion of the coolant flow from tip shelf 34 andsquealer pocket 40 in a predominately axial direction aligned withsuction side 54 streamlines adjacent tip section 42 and trailing edge46, which streamlines are predominately axial in nature. This alignmentof flow f from squealer pocket 40 at trailing edge 46 reduces themagnitude and strength of the tip leakage vortex (or tip leakage vortexsflow), improving efficiency, performance and durability.

FIG. 5B is a perspective view showing tip section 42 of airfoil 21, withsquealer discharge flow channel 70 extending from squealer tip cavity(or squealer pocket) 40 to trailing edge 46. In this configuration, tipshelf 38 extends through region C to extreme trailing edge surface 46,terminating approximately at the downstream intersection of pressuresurface 52 and suction surface 54. That is, in this configuration tipshelf 38 terminates approximately at the location of squealer dischargeflow channel 70.

In some designs, cooling fluid flow from tip shelf 38 and squealerdischarge flow channel 70 merge at or upstream of extreme trailing edgesurface 46. In these designs, squealer discharge flow channel 70discharges a portion of the cooling fluid flow from tip shelf 38 andsquealer pocket 40, so that tip discharge flow f include contributionsof cooling fluid flow from tip shelf 38 and squealer pocket 40.

While this invention has been described with reference to exemplaryembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the spirit and scope of theinvention. In addition, modifications may be made to adapt a particularsituation or material to the teachings of the invention, withoutdeparting from the essential scope thereof. Therefore, the invention isnot limited to the particular embodiments disclosed herein, but includesall embodiments falling within the scope of the appended claims.

1. An airfoil comprising: a leading edge, a trailing edge and pressureand suction surfaces defining a chord length therebetween, the pressureand suction surfaces extending from a root section of the airfoil to atip section of the airfoil; a tip shelf formed along the tip section ofthe airfoil between the pressure surface and a tip shelf wall spacedbetween the pressure surface and the suction surface, wherein the tipshelf extends from within 10% of the chord length measured from theleading edge to within 10% of the chord length measured from thetrailing edge; and a squealer pocket formed along the tip section of theairfoil between the tip shelf wall and a squealer tip wall extendingfrom the suction surface, wherein the squealer pocket extends fromwithin 10% of the chord length measured from the leading edge toterminate between 10% and 25% of the chord length measured from thetrailing edge.
 2. The airfoil of claim 1, wherein the tip shelf extendsfor more than 90% of the chord length.
 3. The airfoil of claim 1,wherein the tip shelf extends for more than 95% of the chord length. 4.The airfoil of claim 1, wherein the tip shelf extends from a locationwithin 5% of the chord length measured from the leading edge of theairfoil to a location within 5% of the chord length measured from thetrailing edge of the airfoil.
 5. The airfoil of claim 1, wherein the tipshelf extends around the leading edge and onto the suction surface. 6.The airfoil of claim 1, wherein the tip shelf extends to an intersectionof the pressure surface and the suction surface at the trailing edge. 7.The airfoil of claim 1, wherein the squealer pocket extends for morethan 75% of the chord length and less than 90% of the chord length. 8.The airfoil of claim 7, wherein the squealer pocket extends from alocation within 5% of the chord length measured from the leading edge ofthe airfoil.
 9. The airfoil of claim 1, further comprising a squealerdischarge flow channel extending from the squealer pocket to thetrailing edge of the airfoil.
 10. The airfoil of claim 1, furthercomprising a plurality of cooling holes formed in the tip shelf togenerate cooling fluid flow along pressure surface of the airfoil. 11.The airfoil of claim 10, further comprising a plurality of cooling holesformed in the squealer pocket to generate cooling fluid flow along thetip section of the airfoil.
 12. A turbine engine comprising the airfoilof claim
 1. 13. The turbine engine of claim 12, wherein the squealerpocket and tip shelf are configured to match transient response rates ofthe tip section with the pressure and suction surfaces adjacent the tipsection based on removal of metal volume from the tip section of theairfoil, reducing transient thermal strains as compared to an airfoilwithout the squealer pocket and tip shelf.
 14. A gas turbine engineblade comprising: an airfoil comprising convex and concave surfacesextending from a root section to a tip section and from a leading edgeto a trailing edge, the leading and trailing edges defining a chordlength therebetween; a tip shelf defining an open perimeter recessbetween the concave surface and a tip shelf wall spaced between theconvex surface and the concave surface, wherein the open perimeterrecess extends from a region within 5% of the chord length measured fromthe leading edge of the airfoil to a region within 5% of the chordlength measured from the trailing edge of the airfoil; and a squealerpocket defining a closed perimeter recess between the tip shelf wall anda squealer tip wall extending congruently from the convex surface,wherein the closed perimeter recess extends from a region within 5% ofthe chord length measured from the leading edge of the airfoil toterminate in a region between 10% and 25% of the chord length measuredfrom the trailing edge of the airfoil.
 15. The blade of claim 14,wherein the open perimeter recess defined by the tip shelf extends alongthe concave surface of the airfoil for more than 95% of the chordlength.
 16. The blade of claim 15, wherein the closed perimeter recessdefined by the squealer pocket extends along the tip section of theairfoil for more than 75% of the chord length and less than 90% of thechord length.
 17. The blade of claim 16, wherein the open perimeterrecess defined by the tip shelf extends along the concave surface of theairfoil from a region within 2% of the chord length measured from theleading edge of the airfoil to a region within 2% of the chord lengthmeasured from the trailing edge of the airfoil.
 18. The blade of claim14, wherein the open perimeter recess defined by the tip shelf extendsfrom an intersection of the convex and concave surfaces at the trailingedge and around the leading edge of the airfoil onto the convex surface.19. The blade of claim 14, further comprising a plurality of coolingholes formed in the tip shelf to maintain a pocket of cooling fluidalong the tip section of the airfoil between the tip shelf wall and theconcave surface.
 20. The blade of claim 19, further comprising aplurality of cooling holes formed in the squealer pocket to maintain apocket of cooling fluid along the tip section of the airfoil between thetip shelf wall and the squealer tip wall.
 21. An airfoil for a gasturbine engine, the airfoil comprising: leading and trailing edgesextending from a root section to a tip section; pressure and suctionsurfaces defining a chord length between the leading and trailing edges;a squealer tip cavity extending along the tip section of the airfoil,the squealer tip cavity defined between a squealer tip wall extendingcongruently from the suction surface and a tip shelf wall extendingbetween the squealer tip wall and the pressure surface, wherein thesquealer tip cavity extends from a location within 10% of the chordlength measured from the leading edge of the airfoil and terminates in aregion between 10% and 25% of the chord length measured from thetrailing edge of the airfoil; and a tip shelf recess formed between thetip shelf wall and the pressure surface of the airfoil, the tip shelfrecess extending from a location within 5% of the chord length measuredfrom the leading edge of the airfoil to a location within 5% of thechord length measured from the trailing edge of the airfoil.
 22. Theairfoil of claim 21, wherein the tip shelf recess extends from alocation within 2% of the chord length measured from the leading edge ofthe airfoil to a location within 2% of the chord length measured fromthe
 23. The airfoil of claim 21, further comprising a plurality ofcooling holes formed along the squealer tip cavity and a plurality ofcooling holes formed along the tip shelf recess.
 24. The airfoil ofclaim 21, further comprising a squealer discharge flow channel extendingfrom the squealer tip cavity to the trailing edge of the airfoil.
 25. Arotor blade comprising the airfoil of claim
 24. 26. A gas turbine enginecomprising the rotor blade of claim
 25. 27. The gas turbine engine ofclaim 26, wherein the squealer discharge flow channel is configured toreduce tip leakage vortex flow by axially aligning squealer dischargeflow at the trailing edge of the airfoil.
 28. The gas turbine engine ofclaim 26, wherein the tip shelf extends to the trailing edge of theairfoil to terminate at a downstream intersection of the pressure andsuction surfaces.
 29. The gas turbine engine of claim 28, whereincooling fluid flow from the tip shelf and squealer pocket merge at thedischarge flow channel.
 30. The gas turbine engine of claim 29, whereinthe squealer discharge channel is configured to reduce penetration ofleakage flow over the blade tip by discharging cooling fluid flow fromthe tip shelf and the squealer pocket in an axial direction aligned withsuction side streamlines adjacent the tip section of the airfoil at thetrailing edge.